Many of today’s cosmetics can act as vectors for potentially serious infections. A study published in the Journal of Applied Microbiology found that 79% to 90% of in-use makeup has become contaminated with infectious microbes, including E. coli, staphylococci and fungi, which can trigger rashes, skin and respiratory infections or gastrointestinal distress that could become antimicrobial-resistant.

How does this happen? Many users don’t make sure their hands are clean before applying makeup, and they never clean sponges and brushes used to apply makeup; 64% said they drop them on the floor and reuse them without a thought. Foam sponges are especially vulnerable since they absorb moisture that can become a breeding ground for bacteria.

To avoid infections, clean cosmetic brushes and sponges with soap and warm water frequently. Avoid dipping fingers directly into bottles or onto powders/blushes, as that can introduce bacteria into the product. Also, be mindful of makeup’s expiration date. Foundations are generally good for less than a year. Eye makeup like mascara and eyeliner should be replaced every four months to avoid eye infections. Lipstick and lip gloss should be replaced every six months or more often. Finally, trust your senses. If something seems off, toss it.

Mehmet Oz, M.D., is host of “The Dr. Oz Show,” and Mike Roizen, M.D., is chief wellness officer and chairman of the Wellness Institute at Cleveland Clinic. Email questions to youdocsdaily@sharecare.com.